1. Field of the Invention
The present invention relates to a retransfer printing met-hod and a printing apparatus thereof, wherein an ink image is transferred from an ink ribbon to an intermediate transfer film, and then a transfer layer formed on the intermediate transfer film through the transfer process is re-transferred to a printing medium to be printed.
2. Description of the Related Art
A so-called retransfer printing apparatus has been commonly known until now. The retransfer printing apparatus prints such that an ink image is once transferred from an ink ribbon to an intermediate printing film, and then the ink image is re-transferred from the intermediate transfer film to a surface of a printing medium such as a card and a sheet. There exists a card printer,as one example of such a retransfer printing apparatus.
In the case of the retransfer printing method, by using an ink ribbon continuously formed with ink areas of each color such as yellow, magenta, cyan and black that are sequentially arranged on a belt-shaped sheet, heating a thermal head in response to a picture image transfers ink from each ink area to an intermediate transfer film and forms the picture image on the intermediate transfer film. Then the picture image formed on the intermediate transfer film is re-transferred to a printing medium by applying heat and pressure of a heat roller and finally printed on the printing medium.
In the case that a printing medium is in a shape of a bankbook or a card, there provided an area for an IC chip, a magnetic stripe or writing a signature on the surface of the printing medium.
If any membrane is adhered over the area provided as mentioned above while re-transferring, there exist problems. In the case that the area is for an IC chip, terminals for external connection of the IC chip are made poor contact. In the case that the area is a magnetic stripe area, poor contact with a magnetic head occurs. In the case that the area is for signature, ink of a ball point pen or like hardly fixes permanently in the area.
In order to solve the above-mentioned problems, by designating such an area to be a non-transfer area so as not to be transferred while re-transferring, various countermeasures have been studied such that a shape of a heat roller was designed and an area for not forming an ink image corresponding to a non-transfer area was provided on an intermediate transfer film. However, in any cases, these countermeasures resulted in increasing cost drastically because a special component varied by each picture image to be printed was essential to be exclusively prepared.
With respect to these problems, the Japanese Patent Application Laid-open Publication No. 7-266589/1995 discloses the method that is capable of forming a desired non-transfer area without using a special component.
The method disclosed in the Japanese Patent Application Laid-open Publication No. 7-266589/1995 is as follows: a peeling layer (adhesive layer) is continuously provided on each ink layer of an ink ribbon so as to peel off ink that is transferred on an intermediate transfer film, and at the end of a transfer process of one image, ink that is previously transferred on the intermediate transfer film is peeled off by heating an area corresponding to a non-transfer area of the peeling layer by means of a thermal head, and then the non-transfer area is formed on the intermediate transfer film.
Consequently, a non-transfer area is enabled to form on an intermediate transfer film by designating an arbitrary range.
In the meantime, whether or not a peeling layer enables to peel off ink transferred on an intermediate transfer film depends upon whether or not a desired range of the peeling layer enables to be heated up to a predetermined temperature or more.
However, when heating a thermal head, a gradient of rising temperature of the thermal head is gradual and there exists scatter in a rising temperature characteristic of each modular head of the thermal head, wherein modular heads are arranged in line and in parallel with each other. Consequently, a boundary to be a non-transfer area is hardly designated, and resulting in a problem of peeling off ink defectively.
Further, such defective peeling off was particularly remarkable at a border where a relative position of a thermal head on an ink ribbon moved from a transfer area to a non-transfer area when transferring.